The present invention relates generally to fluid delivery devices. In particular, it is concerned with a self-contained fluid delivery device that can be used to deliver a variety of medications at a selectable flow rate, and which may include a bolus port for intermittent immediate controlled delivery of additional doses of fluid.
Diabetes is a chronic disease that is caused by both hereditary and environmental factors. It is characterized by the body""s inability to control glucose levels. Left untreated, it causes damage to the circulatory and nervous systems and results in organ failures, amputations, neuropathy, blindness and eventually death. It has been definitively shown that the cost of the complications related to diabetes significantly exceeds the cost of therapy. The Diabetes Control and Complications Trial (DCCT) was a ten-year study of 1400 patients to assess the benefits of close control of blood glucose levels. The study found that such close control provided 50% to 75% reductions in retinopathy, neuropathy, neuropathy and cardiovascular risk.
There are roughly 17.5 million people with diabetes in the United States and Europe, and about 60 million more worldwide. Roughly 35% of these people use insulin to maintain close control of their glucose levels. Proper control of blood glucose levels through programmed insulin injection or infusion allows a high quality of life and a life expectancy of an additional 35 to 40 years from diagnosis.
Currently, there are two principal modes of daily insulin therapy. The first mode includes syringes and insulin pens. These devices are simple to use and are relatively low in cost, but they require a needle stick at each injection, typically three to four times per day. The second is infusion pump therapy, which entails the purchase of an expensive pump that lasts for about three years. The initial cost of the pump is a high barrier to this type of therapy. From a user perspective, however, the overwhelming majority of patients who have used pumps prefer to remain with pumps for the rest of their lives. This is because infusion pumps, although more complex than syringes and pens, offer the advantages of continuous infusion of insulin, precision dosing and programmable delivery schedules. This results in closer glucose control and an improved feeling of wellness.
The typical patient on intensive therapy injects insulin to provide a basal level and then takes supplemental boluses prior to meals during the day. Those on infusion pumps program their pumps to mimic this type of delivery schedule. There are several existing or anticipated means of insulin therapy that a patient might consider.
The first are so-called oral agents that enhance the ability of the body to utilize insulin. Typical compounds include sulfonylureas, biguanides and thiazolidinediones. Oral agents are initially appropriate for Type 2 diabetics, whose bodies produce some insulin, although after a period of years these patients generally need to supplement with additional insulin. For Type 1 diabetics, the body does not produce insulin and these agents are not effective.
Once the oral agents are no longer effective, insulin is injected using syringes or multi-dose insulin pens. The syringe is the least expensive means of delivery, but many patients are willing to pay a premium for the convenience of the insulin pen.
A recent advance has been the development of extremely long-acting insulins. While regular insulins have a physiological onset in 10 minutes and peak activity in about 90 minutes, current long-acting insulins peak in toughly 8 hours. This type of insulin can be taken in the morning and can be accompanied by bolus delivery at meals. The alternative of simply taking all of one""s insulin requirement in basal delivery is believed by many to be therapeutically unsound. Insulin resistance is theorized to build as a result of high concentrations of insulin in the bloodstream, and as a result ever increasing amounts of insulin are necessary to control blood glucose levels. Unfortunately, the basal plus bolus profile still results in the same high and undesirable frequency of injections, typically four per day. Long-acting insulin does provide good therapy for those patients whose bodies benefit from supplemental basal insulin, but this is a temporary condition and simply delays a more rigorous insulin injection regimen for six months to two years.
As their interest in intensive therapy increases, users typically look to insulin pumps. However, in addition to their high cost (roughly 8 to 10 times the daily cost of syringe therapy) and limited lifetime, insulin pumps represent relatively old technology and are cumbersome to use. Also, from a lifestyle standpoint, the tubing (known as the xe2x80x9cinfusion setxe2x80x9d) that links the pump with the delivery site on the user""s abdomen is very inconvenient and the pumps are relatively heavy, making carrying the pump a bother.
A new method of insulin delivery currently undergoing development is pulmonary delivery. The principal issue with pulmonary delivery is criticality of dose, as pulmonary delivery is relatively inefficient and difficult to quantify. As a result, it will be difficult to keep blood glucose levels in control with this delivery form, although it may prove very useful as a supplement for bolus delivery at mealtime. The inefficiency of delivery (currently about 10%) significantly drives up the cost of pulmonary therapy. The implications of chronic inhalation of insulin are also unknown.
In summary, patients on oral agents eventually move to insulin, and existing pump therapy is very expensive. Interest in better therapy is on the rise, accounting for the observed growth in pump therapy and increased number of daily injections. What is needed to fully meet this increased interest is a form of insulin delivery that combines the best features of daily injection therapy (low cost and ease of use) with those of the insulin pump (continuous infusion, precision dosing and variable delivery rates), and that avoids the disadvantages of each. This will allow a greater number of patients to have access to improved insulin therapy at lower cost.
Several attempts have been made to provide ambulatory or xe2x80x9cwearablexe2x80x9d drug infusion devices that are low in cost and convenient to use. Some of these devices are intended to be partially or entirely disposable. In theory, devices of this type can provide many of the advantages of an infusion pump without the attendant cost and inconvenience. Unfortunately, however, many of these devices cannot provide precise control over the flow rate of the drug at a low delivery cost, and are thus not compatible with dose-critical drugs such as insulin. In addition, devices that operate with fixed insulin flow rates may meet cost targets but still require bolus injections at mealtimes. Ultimately, therefore, these existing devices do not represent an optimal alternative to infusion pumps.
The present invention substantially avoids the disadvantages and limitations of the prior art by providing a wearable, self-contained drug infusion device that is simple in construction but is capable of achieving the precise and variable flow rate control needed for dose-critical drugs such as insulin. The flow rate is selectable by the user to accommodate a wide range of individual metabolic rates. The device is significantly less expensive to manufacture than typical insulin pumps because electronic components are not necessary. Furthermore, the device is dependable because it can incorporate a purely mechanical process.
In a preferred embodiment of the invention, the drug infusion device comprises a housing, a reservoir in the housing for containing a supply of fluid, and a cannula (needle) for delivering the fluid to a patient. The device further comprises first and second flow channels for delivering the fluid from the reservoir to the delivery cannula. The first flow channel is arranged in a serpentine pattern to increase its effective length. The cross section of the first channel (also referred to herein as the xe2x80x9cserpentine channelxe2x80x9d) is smaller than the cross section of the second channel. The second channel is further comprised of a plurality of nodes that are in fluid communication with the serpentine channel. The serpentine channel is divided into a number of sections, and each section is associated with a node in the second channel. The nodes can be selectively turned off to allow or prevent fluid from flowing through the node. Thus, when a node is open, fluid is able to pass through the second channel, which imparts less flow restriction due to its larger cross section and shorter length. By closing one or more nodes, fluid flowing from the reservoir to the needle is forced to travel through the portions of the serpentine channel associated with the closed nodes. Closing more nodes increases the effective length of the serpentine channel that the fluid must flow through. Thus, by closing more nodes, the effective length of the serpentine channel is increased, the flow restriction is increased, and the flow rate is decreased.
In a preferred embodiment of the invention, a disc spring (also referred to as a Belleville spring) is included within the housing. When the device is activated, the Belleville spring engages and pressurizes the fluid reservoir, causing the fluid to flow out of the reservoir and toward the needle. The Belleville spring applies constant pressure on the reservoir, causing the flow rate to remain constant over time despite changes in the fluid volume in the reservoir.
In another preferred embodiment, the first and second channels are formed in the housing, with one wall of the channels being formed by a flexible membrane that is fixedly attached to the housing. The nodes of the second flow channel are defined by indentations in the housing along the second flow channel. A flow rate selection device is movably attached to the housing, such that the flexible membrane is sandwiched between the housing and the flow rate selection device. The flow rate selection device is provided with detents which correspond in shape to the indentations in the housing. The flow rate selection device may be moved into alignment with the indentations so that a selected number of detents aligns with corresponding indentations. Because the shape of the detents matches the indentations, the detents push the flexible membrane into the indentations, preventing the flow of fluid through the nodes. Thus, the detent, membrane and indentation act like a valve at each node.
In another preferred embodiment the device is provided with a bolus port for delivering a bolus injection of medicament. The port comprises an opening in the housing in communication with the proximal end of the delivery cannula. The opening is preferably sealed with an elastomeric septum so that a syringe may be used to deliver an additional dose of medicament through the port to the user immediately. When the bolus injection is completed and the syringe is removed, the septum reseals, preventing medicament from escaping through the bolus port and maintaining the hermetic seal around the device. The bolus port may also include a cone shaped guide for guiding the needle of the syringe to the membrane.